Rotationally driven multi-bevel step tool

ABSTRACT

The invention relates to a rotationally driven multi-bevel step tool, particularly a step drill for drilling into solid material, comprising a plurality of one-edged or multi-edged cutting steps which are arranged in a staggered manner in the cutting and advancing directions and each have a number of flutes that corresponds to the number of edges. Flutes ( 23, 33 ) adjoining each other in the circumferential direction are separated from each other by a web ( 24 ). According to the invention, the flues ( 23, 33 ) adjoining each other in the circumferential direction of two consecutive cutting steps ( 20, 30 ) in the cutting and advancing directions are connected to each other by a metal-cutting window ( 25 ) that is open on the circumferential side and interrupts the interposed web ( 24 ).

The invention relates to a rotationally driven step tool, in particulara step drill for drilling into solid material, with a plurality of ineach case single- or multi-edged cutting steps arranged in a staggeredmanner in the cutting and feed direction according to the preamble ofclaim 1.

Machining operations, which are multi-step, often occur in productiontechnology. So, it is for example a matter of producing axiallystaggered bores of various diameters, but often also bores withcountersinks or combinations of various holes and countersinks. In orderto keep the machining times as low as possible, combination tools weredeveloped in order to produce the previously mentioned various machiningoperations in one work step. Combination tools of this type include stepdrills, countersinks, step countersinks, step reamers, etc., which aregenerally designated—where expedient—as step tools in the following.

Examples for step tools of this type are found in the publisheddocuments DE 299 01 414 U1, DE 36 10 016 A1, DE 200 15 550 U1, DE 202007 015 595 U1, DE 1785012 U or DE 1 041 324 A. In the case of the steptools described in DE 299 01 414 U1, DE 36 10 016 A1 and DE 200 15 550U1, the swarf created in each case in a plurality of cutting steps isconducted away via common flutes. The step tool described in DE 202007015595 U1 has two cutting steps with their own flutes in each case.The step drill described in DE 1 041 324 A is virtually a combination ofthe two previously mentioned step tools, in which three flutes areassigned in each case to a first, third and fifth cutting step and asecond and fourth cutting step. DE 1 785 012 A shows and describes ageneric multi-step tool in the form of a multi-bevel step drill with twocutting steps of various machining diameters, each cutting step beingassigned its own flutes.

Conventional multi-bevel step tools have the disadvantage that underunfavourable conditions, a swarf jam can occur easily in the region of acutting step with relatively small machining diameter due to the factthat the volume available for conducting away swarf for each flute isfor the most part of small dimensions. The risk of a swarf jam increasesfor example with the axial length of a cutting step with small machiningdiameter.

Starting from a multi-bevel step tool, as is known in DE 1 785 012 A,the invention is based on the object of developing a multi-bevel steptool in such a manner that reliable conduction away of swarf is ensured,particularly in the region of a cutting step with a relatively smallmachining diameter.

The object is achieved by means of a multi-bevel step tool with thefeatures of claim 1.

The rotationally driven multi-bevel step tool according to the inventionhas a plurality of in each case single- or multi-edged cutting stepsarranged in a staggered manner in the (circumferential or rotational)cutting and (axial or) feed direction with a number of flutescorresponding to the number of cutting edges in each case. In the caseof single-edged cutting steps, the cutting steps therefore haveprecisely one cutting edge in each case as well as a flute assigned tothe cutting edge, whilst in the case of double-, triple-, etc.—edgedcutting steps, the cutting steps have a corresponding number of cuttingedges as well as a number of flutes corresponding to the number ofcutting edges, which flutes are assigned to one cutting edge in eachcase. Each cutting step therefore has a number of flutes correspondingto the number of the cutting edges present in each case. Flutes whichare adjacent in the circumferential direction are delimited from oneanother in each case by means of a web. The flutes and therefore alsothe webs lying therebetween can run helically or linearly in relation tothe rotational axis of the multi-bevel step tool.

In the case of two cutting steps, in the cutting and feed direction, thestaggering of the cutting steps, which have various machining diameters,provides a first or leading cutting step in the cutting and feeddirection with a smaller machining diameter and a second or trailingcutting step in the cutting and feed direction with a larger machiningdiameter. In the case of more than two cutting steps, in each case twosuccessive cutting steps in the cutting and feed direction are formed,made up of a leading cutting step in the cutting and feed direction anda trailing cutting step in the cutting and feed direction, for examplethe first cutting step and the second cutting step or the second cuttingstep and the third cutting step, etc. A leading cutting step always hasa smaller machining diameter than a trailing cutting step.

As mentioned above, in the case of the multi-bevel step tool accordingto the invention, flutes, which are adjacent in the circumferentialdirection, of two cutting steps, which follow one another in the cuttingand feed direction, are in each case delimited from one another by aweb. In spite of their assignment to various cutting steps, the flutesare preferably constructed continuously from the start of the respectivecutting step to the outlet at the tool shank, so the flutes of a leadingcutting step are longer than the flutes of a trailing cutting step, aslong as the flutes run out at the same point in the axial direction.

According to the invention, the flutes, which are adjacent in thecircumferential direction, of two cutting steps, which follow oneanother in the cutting and feed direction, i.e. a leading cutting stepwith a smaller machining diameter and a trailing cutting step with alarger machining diameter, are connected via a swarf window whichpenetrates the web lying therebetween and is open on the circumferentialside. With respect to the leading cutting step, the swarf window istherefore located either in the respectively assigned milling face ofthe leading cutting step or else, in case the multi-bevel step tool isformed from a support body equipped with cutting plates, in the face ofthe flute of the leading cutting step which extends the respectivelyassigned milling face.

The cutting steps, which follow one another in the cutting and feeddirections and the flutes of which are adjacent in the circumferentialdirection and are in each case connected by a swarf window, arepreferably the first and second cutting step, as problems conductingaway the swarf have more of a tendency to occur in the region of thefirst cutting step which has the smallest machining diameter.Alternatively or additionally to the first and second cutting steps,flutes, which are adjacent in the circumferential direction, of thesecond and third steps, the third and fourth steps, etc., i.e. any twocutting steps which follow one another in the cutting and feeddirection, can also be connected by a swarf window in the web locatedtherebetween, however.

In each case, at least a portion of the swarf which is conducted away inthe flute of a leading cutting step in the cutting and feed directionwith a smaller machining diameter can escape via the swarf window, whichis produced e.g. by milling out or grinding out, into the flute, whichis adjacent in the circumferential direction, of a trailing cutting stepin the cutting and feed direction with a larger machining diameter. Theconducting away of the swarf produced in the leading cutting steptherefore takes place in the direction of extension of the flutes untilthe swarf window is reached only via the respective flute of the leadingcutting step and from the reaching of the swarf window both in therespective flute of the leading cutting step and in the flute of thetrailing cutting step, which is adjacent in the circumferentialdirection. Therefore, overall an enlarged volume is available forconducting away swarf created in a leading cutting step, as a result ofwhich an improved conduction away of swarf can be achieved, especiallyin the case of a very small machining diameter of a leading cuttingstep. Thanks to the improved conduction away of swarf, if appropriate,the radial depth of the flute(s) of the leading cutting step can bedimensioned narrowly, in order, e.g. to obtain a large core diameter.

The multi-bevel step tool is used in particular in the form of amulti-bevel step drill for producing injector bores in a cylinder head.The individual cutting steps, for example three cutting steps, arepreferably constructed in a multi-edged manner in each case with frontand circumferential cutting edges equidistantly arranged in thecircumferential direction, particularly in a double-edged manner withfront and circumferential cutting edges arranged point-symmetrically.

Further advantageous developments are the subject matter of dependentclaims.

In a preferred development, the swarf window extends in the radialdirection essentially as far as the base of the flute, which is adjacentin the circumferential direction, of the trailing cutting step. Theswarf window therefore has a satisfactory radial depth which means thatthe swarf produced in the leading cutting step can pass over into theflute, which is adjacent in the circumferential direction, of thetrailing cutting step and can there be forwarded in the direction of thetool shank.

The swarf window is preferably arranged in such a manner in the feeddirection that it encompasses at least the start of the trailing cuttingedge, in particular in such a manner that an assigned front cutting edgeof the trailing cutting step is essentially located centrally in theswarf window. With this position, it is ensured the maximum length ofthe flute of the trailing cutting step is available for the furthertransporting of the swarf created in the leading cutting step. The swarfescaping from the flute of the leading cutting step via the swarf windowinto the flute, which is adjacent in the circumferential direction, ofthe trailing cutting step is therefore conducted from the start of thetrailing cutting step together with the swarf produced in the trailingcutting step in the direction of the tool shank.

The radial depth and also the axial length, i.e. the size of the swarfwindow can be determined as a function of the material to be machinedand/or the average size (length, thickness, width) of the swarf to beexpected in the leading cutting step. Actually, this means that in thecase of relatively long swarf, a deeper longer swarf window can beprovided, whilst in the case of relatively short swarf, a flattershorter swarf window may be sufficient. By means of a shaping of theswarf window which takes account of the respective productionconditions, the passing over of the swarf from the flute of the leadingcutting step into the flute, which is adjacent in the circumferentialdirection, of the trailing cutting step can be improved.

The swarf window is divided in the axial direction of the tool tip inthe direction of the tool shank preferably into a swarf window inlet ofincreasing radial depth, a swarf window base, which is adjacent to theswarf window inlet and preferably runs axially parallel, and a swarfwindow outlet of decreasing radial depth, which is adjacent to the swarfwindow base. The length of the preferably axially parallel running swarfwindow base can be determined in accordance with the respectiverequirements. For example, the swarf window base can be dimensioned in avery short manner, as a result of which the swarf window has the shapeof a concave recess when observed from the side. By means of a longerdimensioning of the swarf window base, the swarf window can have anelongated shape. The swarf window inlet and the swarf window outlet arepreferably in each case constructed as concavely curved surfaces. Theswarf window base is preferably formed from a planar surface ofpredetermined axial length or from a for example concavely curvedsurface of predetermined axial length.

The swarf window base is preferably inclined by an predetermined anglewith respect to the milling face or a flute face, which extends themilling face of the trailing cutting step, of the flute, which isadjacent in the circumferential direction. By means of the inclinationof the swarf window base with respect to the milling face or a fluteface, which extends the milling face, of the flute, which is adjacent inthe circumferential direction, of the trailing cutting step, thedifference in the radial depth between the flute of the leading cuttingstep and the flute of the trailing cutting step can be graduallyreduced, as a result of which the spilling over of the swarf from theflute of the leading cutting step into the flute, which is adjacent inthe circumferential direction, of the trailing cutting step is improved.

Further, the swarf window can be orientated in the direction of theopening through the web located between the flutes which are adjacent inthe circumferential direction essentially radially with respect to therotational axis of the multi-bevel step tool or with respect to thedirection of longitudinal extent of the two flutes or else at an anglesmaller than 90° relative to the rotational axis of the multi-bevel steptool or relative to the direction of longitudinal extent of the flute ofthe respectively trailing cutting step. The orientation of the swarfwindow at an angle smaller than 90° relative to the rotational axis ordirection of longitudinal extent of the flute is advantageous comparedto an essentially radial orientation to the extent that the swarf isdeflected to a lesser extent through the swarf window from the flute ofthe leading cutting step into the flute, which is adjacent in thecircumferential direction, of the trailing cutting step, as a result ofwhich the conducting away of swarf is improved overall.

In a preferred development, the multi-bevel step tool according to theinvention has an integrally constructed support body made from solidcarbide and PCD (polycrystalline diamond) cutting plates arranged on thesupport body. In this development, the swarf window of the leadingcutting step is adapted with respect to axial length and axial positionto the axial length and axial position of an assigned cutting plate ofthe trailing cutting step.

The flutes can be spirally constructed, preferably they are linearlyconstructed however.

The multi-bevel step tool according to the invention further preferablyhas an internally located channel system designed for minimum quantitylubrication for providing one or a plurality of cutting steps withcoolant/lubricant. The coolant/lubricant supply in this case preferablytakes place via discharge openings which are in each case located in theregion of a front open area, i.e. in the cutting direction behind anassigned front cutting edge of the leading cutting step. In the case ofa multi-bevel step tool with a plurality of cutting steps, it may besatisfactory if only certain cutting step(s), for example in the case ofthree cutting steps only the first and second cutting steps, the swarfof which must be conducted away over a relatively long path in thedirection of the tool shank, are provided with lubricant. In each case,the lubricant leaving at the front in the region of the open area canflow away via the flute, which is adjacent in the circumferentialdirection, of the trailing cutting step in the cutting direction andthereby support the conducting away of swarf in the trailing cuttingstep.

In the following, an exemplary embodiment of a multi-bevel step toolaccording to the invention is explained on the basis of drawings. In thefigures:

FIG. 1 a shows a side view of an embodiment of a multi-edged step drill;

FIG. 1 b shows a frontal view of the step drill from FIG. 1 a;

FIG. 2 a shows a side view of the step drill rotated through −40° aboutthe rotational axis compared to the side view according to FIG. 1 a;

FIG. 2 b shows a frontal view of the step drill rotated through −40°about the rotational axis compared to the frontal view according to FIG.1 b

FIG. 3 a shows a side view of the step drill rotated through −70° aboutthe rotational axis compared to the side view according to FIG. 1 a;

FIG. 3 b shows a frontal view of the step drill rotated through −70°about the rotational axis compared to the frontal view according to FIG.1 b;

FIG. 3 c shows a view on an enlarged scale of the tool tip of the stepdrill from FIG. 3 a; and

FIG. 4 shows a perspective illustration of the step drill according tothe FIGS. 1 a to 3 c.

In the figures, a multi-edged, machining and rotationally drivenmulti-bevel step tool in the form of a step drill is specified with thereference number 10. The step drill 10 is used for producing steppedbores, as are required for example as injector bores in cylinder blocksin automotive technology for accommodating fuel injectors. It is pointedout that the dimension and machining information contained in thefigures relates to just one exemplary embodiment of a multi-bevel steptool.

The step tool 10 has a tool shank 12 for clamping in a chuck (not shown)and a cutting part 14. The step drill 10 for example has a length ofapprox. 191.5 mm and a tool shank diameter of approx. 25 mm. In theexemplary embodiment shown, the step drill 10 has three cutting steps20, 30 and 40, the first cutting step 20 having a nominal diameter D20,the second cutting step 30 having a somewhat larger nominal diameter D30and the third cutting step 40 having an in turn larger nominal diameterD40.

The dimension D20 is for example approximately 7.7 mm, the dimension D30is approximately 18 mm and the dimension D40 is approximately 23.7 mm.All of the nominal diameters are of exceptionally narrow tolerance. Thefirst, second and third cutting steps 20, 30, 40 are, as can be seenfrom the figures, arranged in a staggered manner in the cutting and feeddirection, specifically in such a manner that the angular spacingbetween the first and the second cutting steps is approximately −40° andthe angular spacing between the first and the third cutting steps isapproximately −70°. In the FIGS. 1 a, 2 a, the start of the second andthird cutting steps 30, 40 is in each case indicated by means of dashedlines.

The first, second and third cutting steps 20, 30, 40 are double-edged ineach case in the exemplary embodiment shown, i.e. constructed with twofront cutting edges 21, 31, 41 and two circumferential cutting edges 22,32, 42 in each case, as well as with two flutes 23, 33, 43 in accordancewith the number of cutting edges in each case (cf. FIG. 1 b, FIG. 2 b).The flutes 23, 33, 43 are, as can be seen from the figures, in each caseconstructed continuously and linearly from the start of the respectivecutting step 20, 30, 40 to the outlet thereof shortly upstream of thetool shank 12. Flutes 23, 33 or 33, 43 adjacent in the circumferentialdirection are delimited from one another in each case by means of a web24, 34, 44. Due to the staggering of the first, second and third cuttingsteps 20, 30, 40 in the cutting and feed direction, as can be seen fromthe figures, the first cutting step 20 forms a leading cutting step inthe cutting and feed direction with respect to the second cutting step30, whilst the second cutting step 30 forms a trailing cutting step inthe cutting and feed direction with respect to the first cutting step 20and also forms a leading cutting step with respect to the third cuttingstep 40. The third cutting step 40 in turn forms a trailing cutting stepin the cutting and feed direction with respect to the second cuttingstep 30.

In the exemplary embodiment shown, the step drill 10 has an integrallyconstructed support body made from solid carbide and PCD(polycrystalline diamond) cutting plates 14, 15, 16 arranged on thesupport body, which in each case form a front and a circumferentialcutting edge 21, 22, 31, 32 or 41, 42 (cf. FIG. 3 c).

In the exemplary embodiment shown in the figures, the flutes 23, 33,which are adjacent in the circumferential direction, of the first andsecond cutting steps 20, 30 are connected to one another by means of aswarf window 25 which penetrates the web 24 located therebetween and isopen on the circumferential side. In the exemplary embodiment shown, theswarf window 25 which penetrates the web 24 extends in the radialdirection essentially as far as the base of the flute 33, which isadjacent in the circumferential direction, of the trailing secondcutting step 30. The swarf window 25 extends in the feed direction asfar as the start of the second cutting step 30, specifically essentiallyso far that the closest front cutting edge 31 of the second cutting step30 is located essentially centrally in the swarf window 25 (cf. FIG. 2a).

The swarf window 25 is divided in the axial direction of the tool tip 11in the direction of the tool shank 12 into a swarf window inlet 25 a ofincreasing radial depth, a swarf window base 25 b, which is adjacent tothe swarf window inlet 25 a and runs axially parallel, and a swarfwindow outlet 25 c of decreasing radial depth, which is adjacent to theswarf window base 25 b (cf. FIGS. 3 a, 3 c). In the exemplary embodimentshown, the swarf window inlet 25 a and the swarf window inlet 25 c withthe swarf window base 25 b located therebetween construct a swarf windowin such a manner that the swarf window 25 is essentially radiallyorientated in the direction of the opening through the web 24 relativeto the rotational axis 11 of the step drill or relative to the directionof longitudinal extent of the flute 33 of the second cutting step 30(cf. in FIG. 3 c: α≈=90°.

In the exemplary embodiment shown, the length of the axially parallelrunning swarf window base 25 b essentially corresponds to the length ofthe PCD cutting plate 15 which forms the front and circumferentialcutting edges 31, 32 of the second cutting step 30. The swarf windowinlet 25 a and the swarf window outlet 25 b are in each case constructedas concavely curved surfaces. In the exemplary embodiment shown, theswarf window base 25 b is formed from a planar surface of predeterminedaxial length. Furthermore, the swarf window base 25 b is inclined by anpredetermined angle, of approximately 5° in the exemplary embodimentshown, with respect to a flute face 36, which extends the milling face35 of the second cutting step 30, of the flute 33.

The tool 10 has a coolant/lubricant supply of the first and secondcutting steps 20, 30 by means of an internally located channel system 50designed for minimum quantity lubrication, which is indicated dashed inFIG. 1 a. The coolant/lubricant supply takes place via dischargeopenings 28, 38 which are in each case located in the region of a frontopen area 29, 39, i.e. in the cutting direction behind an assigned frontcutting edge 21, 31 of the first or second cutting step 20, 30.

Of course, deviations from the described exemplary embodiments arepossible without abandoning the basic ideas of the invention.

Thus, in the exemplary embodiment shown, swarf windows can be providednot only between the flutes 23, 33, which are adjacent in thecircumferential direction, of the first and second cutting steps 20, 30,but also between the flutes, which are adjacent in the circumferentialdirection, of the second and third cutting steps 30, 40.

Instead of three cutting steps, a multi-bevel step tool according to theinvention can have just two, or else more than three cutting steps. Ifmore than three cutting steps are present, any flutes, which areadjacent in the circumferential direction, of a leading and trailingcutting step in the cutting and feed direction are connected to oneanother by means of a swarf window which penetrates the web locatedtherebetween.

In deviation from the exemplary embodiment shown, in which the swarfwindow 25 is essentially orientated radially to the rotational axis 11or to the direction of longitudinal extent of the flutes of the trailingcutting step in each case, the swarf window inlet 25 a and the swarfwindow outlet 25 c with the swarf window base 25 b located therebetweencan also be constructed in such a manner that the swarf window 25 isorientated at an angle α<90° relative to the rotational axis 11 or tothe direction of longitudinal extent of the flutes of the trailingcutting step in each case.

The various cutting steps can be constructed in a single-edged manner ineach case, in deviation from the exemplary embodiment shown or else havemore than two cutting edges.

Furthermore, instead of a few selected cutting steps, all cutting stepscan also be supplied with coolant/lubricant.

1. A rotationally driven multi-bevel step tool, particularly a stepdrill for drilling into solid material, with a plurality of in each casesingle- or multi-edged cutting steps arranged in a staggered manner inthe cutting and feed direction with a number of flutes corresponding tothe number of cutting edges in each case, wherein flutes which areadjacent in the circumferential direction are delimited from one anotherin each case by means of a web, characterised in that the flutes, whichare adjacent in the circumferential direction, of two successive cuttingsteps are connected to one another by means of a swarf window whichpenetrates the web located therebetween and is open on thecircumferential side.
 2. The multi-bevel step tool according to claim 1,characterised in that the swarf window extends in the radial directionessentially as far as the base of the flute of the trailing cuttingstep.
 3. The multi-bevel step tool according to claim 1, characterisedin that the swarf window extends in the axial direction towards the toolshank at least as far as the start of the trailing cutting step.
 4. Themulti-bevel step tool according to claim 3, characterised in that theswarf window extends in the axial direction towards the tool shank tosuch an extent that a closest front cutting edge of the trailing cuttingstep is located essentially centrally in the swarf window.
 5. Themulti-bevel step tool according to claim 3, characterised in that theswarf window has a predetermined axial length which is determined as afunction of the swarf size of the swarf produced in the leading cuttingstep.
 6. The multi-bevel step tool according to claim 1, characterisedin that the swarf window is divided in the axial direction in thedirection towards the tool shank into a swarf window inlet of increasingradial depth, a swarf window base, which is adjacent to the swarf windowinlet and preferably runs axially parallel, and a swarf window outlet ofdecreasing radial depth, which is adjacent to the swarf window base. 7.The multi-bevel step tool according to claim 6, characterised in thatthe swarf window base is formed from a planar surface.
 8. Themulti-bevel step tool according to claim 6, characterised in that theswarf window base is preferably inclined by an predetermined angle withrespect to the milling face or a flute face, which extends the millingface, of the flute, which is adjacent in the circumferential direction,of the trailing cutting step.
 9. The multi-bevel step tool according toclaim 6, characterised in that the swarf window inlet and the swarfwindow outlet are in each case constructed as concavely curved surfaces.10. The multi-bevel step tool according to claim 1, characterised inthat the swarf window is orientated in the direction of the openingthrough the web located between the flutes which are adjacent in thecircumferential direction at a predetermined angle (α≦90° relative tothe rotational axis of the multi-bevel step tool or relative to thedirection of longitudinal extent of the flutes.
 11. The multi-bevel steptool according to claim 1, characterised by a preferably integrallyconstructed support body made from solid carbide and in that the cuttingedge(s) of the cutting steps are formed by PCD (polycrystalline diamond)cutting plates arranged on the support body.
 12. The multi-bevel steptool according to claim 11, characterised in that the swarf windowcorresponds with respect to axial length and axial position to the axiallength and axial position of a closest cutting plate of the trailingcutting step.
 13. The multi-bevel step tool according to claim 1,characterised in that the flutes are constructed linearly.
 14. Themulti-bevel step tool according to claim 1, characterised by aninternally located channel system designed for minimum quantitylubrication for supplying the multi-bevel step tool withcoolant/lubricant.
 15. The multi-bevel step tool according to claim 14,characterised in that the coolant/lubricant supply of one or a pluralityof cutting steps takes place via discharge openings which are in eachcase located in a front open area behind an assigned front cutting edge.16. The multi-bevel step tool according to claim 1, characterised inthat the cutting steps are constructed in a multi-edged manner in eachcase with front and circumferential cutting edges equidistantly arrangedin the circumferential direction, particularly in a double-edged mannerwith front and circumferential cutting edges arrangedpoint-symmetrically.